Flow prover with seal monitor

ABSTRACT

A flow prover with seal monitor includes a housing with a cylinder and a piston-like displacer sealingly conveyed along the cylinder by the fluid flow to be measured. The displacer includes at least one rod that extends telescopically through the housing. A pair of conduits may be arranged concentrically within the rod, one in communication with a volume between a pair of seals whose integrity is to be monitored and the other in communication with the fluid in the housing. The conduits each communicate as well with a pressure sensor located outside of the housing. The sensor may be mounted on the rod to sense the absence of a pressure differential between the conduits, which indicates a seal failure. The sensor may provide an indication, which may be detected at the end of a proving cycle, that the seal integrity was maintained throughout the proving cycle.

BACKGROUND OF THE INVENTION

This invention pertains to the volumetric measurement of flow and,particularly, a flow prover useful in periodically calibrating acontinuous flow meter in a pipeline without interrupting the flow offluid. The flow prover of this invention falls generally into that classof flow provers characterized by the measurement of the movement of apiston travelling through a cylinder wherein the piston has a pluralityof seals which form a fluid barrier in the annular space between thepiston and the cylinder. This invention pertains specifically to acompact flow prover having means for monitoring the seal integrity.

U.S. Pat. No. 3,738,153 to Simmons discloses a seal monitor for a flowprover using resilient balls. A hydraulic cylinder, used to open andclose passages for the balls, has a seal monitor that detects a pressuredifference between the surrounding fluid and the fluid in the regionbetween a passage and the cylinder piston head. However, in Simmons thepiston head does not slide sealingly along a testing cylinder andtherefore the seals can be monitored while the piston head isstationary.

A flow having means for monitoring the seal integrity of its piston isdisclosed in U.S. Pat. No. 4,372,147 to Waugh. Waugh discloses a flowmeter prover having a measuring conduit coaxially mounted within onouter housing which has fluid apertures adjacent the upstream anddownstream ends of the measuring conduit, a piston mounted within theconduit, an actuating rod axially projecting from the downstream side ofthe piston with the free end of the rod extending through the downsteamend of the outer housing, and piston detection switches spaced along thelength of the measuring conduit. The piston is provided with two sealseach encircling the perimeter of the piston to form an annular cavitybetween the seals. A flexible tube, helically wrapped about the rod, hasone end connected to a passage which is in fluid communication with theannular cavity, and the other end of the flexible tube is connected tothe exterior of the apparatus. During the operation of the prover, fluidleakage past either of the seals causes fluid flow that can be detectedby monitoring the pressure in the flexible tubing by means of theexterior connection to the flexible tubing.

It is believed that there are several disadvantages associated withdevices of the type disclosed in Waugh. One potential disadvantage isthat the flexible tubing is cycled with the reciprocating piston, andover a period of time this may ultimately lead to a failure of theflexible tube. Another potential disadvantage is that the differentialpressure between the flexible tubing and the apparatus fluid may resultin collapse or rupture of the tubing. Still another potentialdisadvantage is that a pressure source or a bleed system may berequired. In either case, seal monitoring is complicated by the movementof the seals past the fluid apertures in the measuring conduit. When theintegrity of the seals is monitored dynamically during a proving run, acontrol system to rapidly increase pressure or bleed the flexible tubingafter it moves past the fluid apertures may be required so that adecrease or increase in pressure in the flexible tubing may be observedbefore the proving run is completed. Moreover, it is believed thatduring the pressuring or bleeding, fluid leakage past the seals may notbe detected.

It is a feature of this invention to provide a flow prover having meansfor monitoring the seal integrity of the flow prover piston whichovercomes many of the disadvantages associated with known devices.

SUMMARY OF THE INVENTION

The flow prover of this invention determines the rate of flow bymeasuring the time in which a displacer travelling through a cylinderdisplaces a known volume of fluid. The flow prover of this invention isprovided with means for monitoring the seal integrity of the displacer.

The flow prover of this invention comprises a measuring cylinder and adisplacer or piston movably disposed within the cylinder. The cylindermay be filled with a fluid whose flow rate is to be measured by theprover. The displacer, provided with two seals, forms a fluid barrier inthe cylinder when it is disposed within the cylinder. The seals aremechanically compressible and the flow prover is operable to form anannular volume of pressurized fluid defined by the seals, the displacerand the cylinder. A first conduit is positioned parallel to the axis ofthe cylinder. One end of the conduit is attached to the displacer andthe free end is accessible externally from the flow prover. The conduithas a coaxial channel of substantially uniform diameter which permitsfluid communication between the ends of the conduit, and the channel isin fluid communication with the annular volume. The flow prover isprovided with a second conduit which is located in the channel of thefirst conduit. The second conduit is in fluid communication with thefluid in the cylinder and is accessible from the free end of the firstconduit. Means are also provided for measuring the differential pressurebetween the first and second conduits.

The flow rate can be determined by measuring the time in which thedisplacer displaces a predetermined volume of fluid. Any inaccurracyintroduced by the leakage of the fluid past the displacer seals iseasily detected. Since the annular volume between the seals is in fluidcommunication with the first conduit, its pressure can be monitored.Similarly, the pressure of the fluid in the cylinder is monitored bymonitoring the pressure in the second conduit. If the seal integrity ismaintained, the mechanical compression of the seals results in a higherfluid pressure in the annular volume than in the cylinder, and thispressure differential is maintained until the seals are decompressed. Ifthe seal integrity is lost, fluid leakage past either of the sealscauses a decrease in the pressure differential between the annularvolume and the cylinder fluid.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a partial, partially sectioned cross-sectional view of oneembodiment of the compact flow prover of this invention;

FIG. 2 is an enlarged partial cross-sectional view showing the portionof FIG. 1 including displacer seals;

FIG. 3 is an enlarged cross-sectional view through the pressure sensortransverse to the plane of FIG. 1 with the detector rod telescopedinwardly into the prover housing to align with the detector; and

FIG. 4 is a cross-sectional view taken generally along the line 4--4 inFIG. 3.

DESCRIPTION OF A PREFERRED EMBODIMENT

Referring to the drawing wherein like reference characters are used forlike parts throughout the several views, a flow prover 10, shown in FIG.1, includes an displacer housing 12, a piston-like displacer 14, abypass conduit 16, a relatively rigid detecting rod 18 and a reciprocalcylinder 20. The bypass conduit 16 includes an inlet leg 22 with aninlet 24, an outlet leg 26 with an outlet 28 and a normally closedbypass valve 30 between the legs 22 and 26. Liquid, from a pipeline orthe like (not shown), may be inletted to the prover 10 through the inlet24 and returned to the piping or other system through the outlet 28.

The cylinder 20 is conveniently a hydraulic cylinder with a reciprocalpiston 32 having a piston rod 34 extending through a suitable seal 36into the displacer housing 12. More specifically, an end 38 of thepiston rod 34 is fixed to the displacer 14. Thus, when liquid is addedor withdrawn from the cylinder 20 through the action of the hydraulicsystem 21, the piston 32 is displaced, resulting in a correspondingtranslation of the displacer 14. However the cylinder 20 and piston 32may be replaced if desired with a pressure vessel and a hydraulic ram(not shown).

The detecting rod 18 also extends slidably through a seal 40 in thedisplacer housing 12 from an inner end 42, fixed to the displacer 14, toan outer end 44 positioned externally of the housing 12. Thus,reciprocation of the displacer 14 within the housing 12 results intelescoping movement of the rod 18 with respect to its seal 40. Aposition detector 43 is located along the length of the rod 18. Thedetector 43 may take a variety of conventional formats but isconveniently either an optical or magnetic position detecting meanswhereby a flag or other indicator 45 positioned along the rod 18 issensed by appropriate detector elements 47 positioned along a rod 49adjacent the rod 18. In this way the position of the rod 18 with respectto the housing 12 may be determined at the electrical unit 23, which mayinclude a computer and an electronic timer, and more specifically theposition of the displacer 14 with respect to the housing 12 may bemonitored.

The displacer housing 12 includes a pair of enlarged chambers 46, 48 oneither end of a cylinder 50. The chamber 48 communicates with the outletleg 26 while the chamber 46 communicates with the inlet leg 22. Thechambers 46, 48 are of sufficient internal size to permit the fluid toflow around the displacer 14, without obstruction, when the displacer 14is positioned in either chamber 46 or 48. The displacer 14 is providedwith peripheral, resilient annular seals 52 and 54 which are compressedwhen the displacer 14 is positioned within the cylinder 50, as shown inFIG. 1. This compression may be achieved by chamfers 56 and 58 on eitherend of the cylinder 50 adjacent the respective chambers 48 and 46. Withthe seals 52 and 54 in engagement with the cylinder 50, an annularvolume 60 is defined between the seals 52, 54, the displacer 14, and thecylinder 50. This volume 60 communicates by way of a radially orientedpassageway 62 with the interior of the rod 18.

As shown in FIG. 2, the seals 52 and 54 may be U-shaped with inwardlyfacing prongs 51 arranged to be deflected by the inner surface ofcylinder 50. A U-shaped metallic spring member 53 is sandwiched withineach seal 52, 54 by an annular band 55 that is in turn sandwiched by thedisplacer post 57. The seals 52 and 54 are removeably located by guides59 held on the displacer 14 by screws 61.

The displacer 14 is urged into the cylinder 50 by the coil spring 71that encircles a flexible, apertured bearing sleeve 75 in the chamber46. The sleeve 75 is shaped to receive the tapered, forwardly juttingpilot 73 and thus to guide or axially align the rod 34 in the chamber46.

The operation of the displacer 14 and its components is explained ingreater detail in U.S. patent application Ser. No. 546,568, filed Oct.28, 1983, in the name of C. D. Erickson, and in a commonly assignedcontinuation-in-part application, titled "A Compact Flow Prover", Ser.No. 641,029, filed Aug. 15, 1984, and to be Pat. No. 4,549,426 in thename of C. D. Erickson, both of which are hereby expressly incorporatedby reference herein. While the present invention has been described withrespect to a particular arrangement of displacer 14, displacer housing12, and bypass conduit 16, those skilled in the art will appreciate thatthe principles of the present invention may be applied to a variety offlow prover arrangements including that disclosed herein.

The rod 18 includes a relatively rigid first conduit 64 defined withinits interior and a relatively rigid second conduit 66 heldconcentrically within the first conduit 64. The first conduit 64 isdefined by the interior walls of the rod 18, the exterior walls of thesecond conduit 66 and by end seals 68 at each end of the rod 18. Whilethe first conduit 64 is sealed on each end, the second conduit 66 isopen on its inwardmost end 70 to communicate with the interior of thedisplacer housing 12, and conveniently to communicate with the upstreamside of the displacer 14. The first conduit 64 communicates via apassage 65 at an intermediate point along its length with the passageway62 which in turn communicates with the volume 60. The external end 72 ofthe second conduit 66 communicates with a pressure sensor 74, mounted onthe rod 18, while the external end portion 79 of the first conduit 64communicates with a passageway 76 that communicates with the transducer74 by way of a tube 77. Referring to FIG. 3, the transducer 74 isadvantageously a differential pressure sensor with a low pressure port78 in fluid communication with the second conduit 66 and a high pressureport 80 in fluid communication with the first conduit 64.

The sensor 74 may include an externally mounted, broadly circular,rotary indicator 82 with a pie-shaped notch 84 cut from it. A positionsensor 86, shown in FIGS. 1, 3 and 4, is mounted on the cylinder 20,oriented in alignment with the position of the sensor 74 at thecompletion of the proving cycle to detect the rotary position of theindicator 82. The sensor 86 may take a variety of forms including thatof an optical or magnetic position sensor or a linear transducer. Whenan optical system is used, as in the illustrated embodiment, an opposedlight source 91 and receiver 95 may be provided within a U-shapedhousing 93 which straddles the indicator 82, as shown in FIG. 4.Alternatively, the sensor 74 may be adapted to provide a continuouselectrical signal which is proportional to the sensed differentialpressure.

As shown in FIG. 3, the sensor 74 includes a tubular body 88 with anaxial bore 89, a magnetic piston 90, a piston seal 92, a range spring94, and a cylindrical rotary magnet 96. The ends of the bore 89 receivethreaded fittings 98 and 100 with reduced passageways 102. The magneticpiston 90 includes a magnet 104 and a cup-shaped piston element 106shaped to slide along the bore 89. The spring 94 is maintained withinthe interior of the element 106 between a pair of stacking spacers 108and the fitting 100. As the magnet 104 is displaced along the bore 89,due to a pressure differential between the ports 78 and 80, the rotarymagnet 96, held within a transverse bore 110 is rotated. This rotationresults in rotation of the indicator 82 approximately 180° into theposition shown in FIG. 1.

The sensor 74 may be made by modifying the piston type sensor availablefrom Orange Research, Inc., Milford, Conn. It can be readilyappreciated, however, that other types of differential pressure sensors,such as rolling diaphragm sensors or convoluted diaphragm sensors, alsoavailable from Orange Research, Inc., may be used as well.

The compact flow prover 10 may be operated by allowing a fluid, whoseflow rate is to be measured, to flow through the prover 10 such that thedisplacer 14 travels between two predetermined positions in the cylinder50 while the amount of time which is required to traverse this distanceis determined at the electrical unit 23. Specifically, fluid inlettedthrough the port 24 encourages the movement of the displacer 14 from thechamber 46 to the chamber 48 from right to left in FIG. 1. This causesthe rod 18 to telescope further out of the housing 12. The positiondetector elements 47 located along the length of the rod 18 detect theinitial and final positions of the rod 18 and these indications may beused to control an electronic counter (not shown) included within theelectrical unit 23. Based on the time required for the displacer 14 tomove a given distance, the flow rate may be calculated.

The normally closed poppet valve 30 and cylinder 20 are useful inswitching the prover 10 between measuring and retracting modes.Specifically, with the valve 30 in its open position, fluid underpressure may be supplied to the cylinder 20, to return the displacer 14from the chamber 48 back to the chamber 46. The positions of the piston32 and the valve 30 may be controlled by the hydraulic system 21.

The displacer seals 52 and 54 are compressed by the chamfers 56 and 58of the cylinder 50 as the displacer 14 moves into the cylinder 50. Ifthe integrity of the seals 52 and 54 is inviolate, the pressure in thevolume 60 increases as the seals 52, 54 are compressed. Because theannular volume 60 is in fluid communication with the high pressure port80 of the sensor 74, the magnetic piston 90 moves to compress the rangespring 94. This movement of the piston 90 rotates the magnet 96 and theindicator 82. The motion of the indicator 82 is then detected by theposition sensor 86 to indicate that the seals 52, 54 are working. Whenthe displacer 14 is located in either chamber 46 or 48, or when there isa seal leak, the differential pressure is zero and the indicator 82 isnot displaced. When the pressure difference is equalized the spring 94returns the piston 90 to its initial position. With the notch 84positioned upwardly, the light from the source 91 is detected by thereceiver 93.

For optimum reliability, the position sensor 86 is arranged to detectthe rotary indicator 82 in a position which corresponds to thecompletion of the proving cycle, as shown in FIG. 1. In this manner, anyseal failure through the entire proving cycle is indicated by thefailure of the position sensor 86 to detect the presence of the rotaryindicator 82 at the point of insertion of the rod 18 corresponding tothe completion of the proving cycle. In some applications, however, thereliability of this implementation may need to be greater. In theseapplications, the indicator 82 and sensor 86 may be replaced with acontinuous indicator which provides a continuous electrical outputindicative of seal integrity. This may be accomplished in a variety ofways such as by mounting the position sensor 86 on board the rod 18 orthe pressure sensor 74.

In the static method of determining seal integrity the displacer 14 ispositioned within the cylinder 50 with the bypass valve 30 open. Thepressure in the annular space 60 may then be observed for a longerperiod of time. This may be useful since the duration of the provingcycle may be less than 1/3 of a second.

While in the illustrated embodiment, pressure on the downstream side ofthe displacer 14 is compared to pressure between the seals 52 and 54, itis also feasible to measure the pressure on the upstream side. Althoughthe concentric arrangement of the conduits 64 and 66 is advantageous, itis also possible to use a pair of separate, parallel conduits. Inaddition, although a rotary indicator 82 is believed to be advantageous,a variety of other indicators 82 and position sensing systems may beutilized.

The seal integrity monitoring means of the present invention has manyadvantages. The seal monitoring means may have few moving parts. Theconduits 64, 66 may be made from a rigid material which is not subjectto collapse or failure. By placing the differential pressure measuringmeans directly on the free end of the conduits, the seal monitoringmeans may be made entirely self-contained. Then, the seal monitoringmeans may move with the seals being monitored. At the same time thedifferential pressure measuring means are accessible externally from thecompact flow prover and may easily be maintained without disassemblingthe flow prover or removing the displacer. Since the seal monitoringmeans may be entirely self-contained, no double block-and-bleedingsystem on external pressurizing source is required.

While we have described the above specific implementations of ourinvention, many other variations will occur to those skilled in the art.It is intended that all such variations that would fall within the truespirit and scope of the appended claims to be embraced thereby.

What is claimed is:
 1. A flow prover comprising:a measuring cylinderhaving a substantially uniform inside diameter, said cylinder operableto be filled with a fluid whose flow rate is to be measured by saidprover; a displacer movably disposable within said cylinder, saiddisplacer having first and second seal means for forming a fluid barrierin said cylinder, said seal means being compressible to form an annularvolume of pressurized fluid defined by said seal means, said displacer,and said cylinder; a first conduit having a first end attached to saiddisplacer and in fluid communication with said annular volume and asecond end accessible externally of said cylinder; a second conduithaving a first end attached to said displacer and in fluid communicationwith said fluid in said cylinder and a second end accessible externallyof said cylinder; and means located externally of said cylinder formeasuring the differential pressure between said second ends of saidfirst and second conduits, one of said conduits being positionedconcentrically within the other, and said differential pressuremeasuring means being mounted on said conduits.
 2. The flow prover of 1wherein said differential pressure measuring means includes a magneticpiston and a housing, said piston being displaceable within saidhousing, said housing including a magnet displaceable by the motion ofsaid piston within said housing, said magnet having an indicator portionexternal of said housing, said differential pressure measuring meansfurther including position sensing means for detecting the displacementof said indicator portion.
 3. The flow prover of claim 2 wherein saidposition sensing means is arranged to be actuated at an end of a path ofinward movement of said displacer within said cylinder.
 4. The flowprover of claim 2 wherein said indicator portion is a disc with acut-out region.
 5. The flow prover of claim 4 wherein said positionsensing means includes an optical position sensor.
 6. The flow prover ofclaim 1 including means external to said cylinder for detecting theposition of said displacer by detecting the position of the first andsecond conduits.
 7. The flow prover of claim 1 wherein said measuringmeans includes a differential pressure sensor.
 8. The flow prover ofclaim 1 wherein the outer of said conduits is rigid, said cylinderincluding seal means for sealing the point of egress of said outerconduit from said cylinder.
 9. The flow prover of claim 1 wherein saidconduits are relatively rigid and are arranged to sealingly telescopethrough said cylinder.
 10. A flow prover comprising:a measuring cylinderhaving a substantially uniform inside diameter, said cylinder operableto be filled with a fluid whose flow rate is to be measured by saidprover; a displacer reciprocatably disposable within said cylinder, saiddisplacer having first and second seal means for forming a fluid barrierin said cylinder, said seal means being compressible to form an annularvolume of pressurized fluid defined by said seal means, said displacer,and said cylinder; a first conduit having a first end attached to saiddisplacer and in fluid communication with said annular volume and asecond end accessible externally of said cylinder; a second conduithaving a first end attached to said displacer and in fluid communicationwith said fluid in said cylinder and a second end accessible externallyof said cylinder; means located externally of said cylinder for sensingthe differential pressure between said second ends of said first andsecond conduits, said differential pressure sensing means including anindicator portion positioned externally of said housing and adapted tobe displaced in response to differential pressure sensed by saiddifferential pressure sensing means; position sensing means fordetecting the displacement of said indicator portion, said differentialpressure sensing means being connected to said displacer forreciprocation with said displacer, said position sensing means beingstationary such that the differential pressure indicated by saidindicator portion may be detected by said position sensing means whensaid indicator portion is in alignment with said position sensing means.11. The flow prover of claim 10 wherein said differential pressuresensing means includes a magnetic piston and a housing, said pistonbeing displaceable within said housing, said housing including a magnetdisplaceable by the motion of said piston within said housing, saidindicator portion being connected to said magnet.
 12. The flow prover ofclaim 11 wherein said indicator portion is a disk with a cutout region.13. The flow prover of claim 12 wherein said position sensing meansincludes an optical position sensor.
 14. The flow prover of claim 13wherein said disk is rotatable.